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ANALYSIS OF SKIPJACK CATCH PER UNIT OF EFFORT (CPUE) Mark N. Maunder and Simon D. Hoyle

ANALYSIS OF SKIPJACK CATCH PER UNIT OF EFFORT (CPUE) Mark N. Maunder and Simon D. Hoyle.

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ANALYSIS OF SKIPJACK CATCH PER UNIT OF EFFORT (CPUE) Mark N. Maunder and Simon D. Hoyle

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  1. ANALYSIS OF SKIPJACK CATCH PER UNIT OF EFFORT (CPUE)Mark N. Maunder and Simon D. Hoyle

  2. Goal: Develop an index of relative abundance from purse seine catch and effort data on floating objectsProblem: Catch per set is not related to abundance and there is no reliable measure of search timeConcept: The temporal change in the ratio of one species to another in a set is the same as in the population

  3. Main assumption

  4. Known from catch data Known from Stock assessment of species B Unknown Known from catch data The data

  5. GLM approach Known abundance as offset Temporal Effect (i.e. index of relative abundance)

  6. Test • Species of interest: Yellowfin • Species of known abundance: Bigeye • Compare with yellowfin stock assessment estimates of abundance

  7. Application • Species of interest: Skipjack • Species of known abundance: Bigeye • Explanatory variables • Time in months • Latitude • Longitude • Sea-surface temperature • Vessel

  8. Yellowfin results: ratio of YFT to BET

  9. Yellowfin results: Adjusted by BET known abundance

  10. Yellowfin results: Full GLM

  11. Skipjack results

  12. Discussion • The yellowfin test did not validate the method • The known bigeye tuna abundance off set or the GLM did not greatly change the index of relative abundance • The estimated indices of relative abundance are consistent with previous stock assessments and show no major concern for the population

  13. Future work • Incorporate spatial structure or fish size into the analysis • Include other explanatory variables in the analysis (e.g. the catch of other species). • Apply the method to other species

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